<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>

    console.log(typeof Number) // function

    console.log(typeof Math) // object
    console.log(Math)
    console.log(Math.PI)

    var num = 3.55
    console.log(Math.floor(num)) // 3 向下取整
    console.log(Math.ceil(num)) // 4 向上取整
    console.log(Math.round(num)) // 4 四舍五入

    console.log(Math.random()) // [0, 1) 随机数
    console.log(Math.floor(Math.random() * 45) + 5) // [5~50)

  </script>
</body>

</html>